1. Field of the Invention
The present invention is directed to surface cleaning vehicles, and more particularly to a combined single and twin power system for independently driving sweeping machinery of a surface cleaning vehicle.
2. Description of the Related Art
Street cleaning vehicles are well known in the art having mechanical conveying systems, either in the form of a conveyor elevator that drags collected debris up an inclined ramp or via an inclined conveyor belt. The discharge from the conveyor is deposited into a hopper that is provided with a tipping mechanism for discharge.
Street cleaning vehicles employing pneumatic conveying systems are also well known in the art, and fall into two categories, vacuum and regenerative. Both categories of machine employ an exhauster fan to induce high velocity airflow for conveying the debris through a conduit. Regenerative machines additionally utilize the exhauster fan to aid the collection system, whereas vacuum machines do not.
In general, pneumatic conveying systems have a much greater power requirement, as compared to mechanical conveyors, as a result of using the exhauster fan to perform the debris collection and conveying functions. The power requirement for driving the brooms is similar for both types of machines.
The conveying system may be driven either by the prim mover engine used to propel the vehicle—referred to herein as ‘Single’, or by utilizing a separate engine—referred to herein as ‘Twin’.
Single mechanical machines utilize the vehicle's prime moving engine to drive the sweeping mechanisms. More particularly, the sweeping and conveying equipment is hydraulically driven by a pump or pumps coupled to the prime mover engine via a disconnectable power-take-off. The engine and transmission forming part of the carrier vehicle, require little or no change to the driveline and produce sufficient power for the sweeping mechanisms when running at low engine speeds that occur when driving the vehicle slowly, for example at less than 5 MPH (8 km/h). The single machine design enjoys the perception of simplicity in terms of construction and operation. The only criterion of the single design is that, at low speeds, the prime mover engine provides sufficient power to drive the sweeping equipment and perform effectively (i.e. when the vehicle is being driven slowly. Machines of the ‘single’ type have been to be best suited to municipal operations associated with lighter duty street cleaning operations where the machine provides adequate performance (e.g. 40 to 50 Horsepower (30 to 40 kilowatts)) at low operating costs.
Pneumatic machines often incorporate the aforenoted second engine, or ‘twin’ configuration, to drive the sweeping equipment. More particularly, the sweeping and conveying equipment is driven by a mechanical transmission or by a fluid power mechanism powered by a pump or pumps coupled to the second engine. Although there are examples of single engine pneumatic machines, these machines employ auxiliary driveline systems using hydrostatics and/or mechanical gearboxes to enable power to be extracted from the engine at higher speeds whilst maintaining slow sweeping speeds. These modifications greatly increase the cost and complexity of the machine. Moreover, a prime-mover engine of higher than usual power is often required, which tends to further increase the initial cost.
In general, the driveline configuration requirements of the carrier vehicle for a ‘mechanical’ machine are similar to those of a normal commercial transport vehicle with automatic transmission. The vehicle specifications are similar for both the single and twin designs.
The twin design offers more flexibility than the single design in terms of operating modes, since there are no requirements of the prime-mover engine in terms of power or speeds. The sweeping and conveying functions operate independently of how the vehicle is driven, which vary according to the conditions of work (i.e. stop, start, forward, reverse, slow, fast, etc.). By using a second engine, it is possible to design a twin machine with higher sweeping and conveying performance on a given type of vehicle than would be possible with a similar power rating of prime mover engine of single machine design. The flexibility in operation and corresponding sweeping performance are the major advantages of the twin design. These advantages make the twin design best suited to duties associated with industrial activities, road construction and where heavier duty sweeping conditions prevail. The disadvantages are that the machine incurs additional operational costs for fuel and maintenance and there is a perception of increased complexity over single machine design, as a result of using two engines.